#include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;

int main()
{
    long long A,B,N,M;
    cin >> A >> B >> N >> M;
    unsigned long long ans=0;
    ans += min(A,B);
    unsigned long long tmp=0;
    if(A < B)
    {
        while(tmp <= (B-A-tmp)/M) tmp++;
    }
    if(A > B)
    {
        while(tmp <= (A-B-tmp)/N) tmp++;
    }
    ans += tmp-1;
    cout << ans;
    
    return 0;
}